I'm not familiar with your boat, but I have replaced 2 transoms without ever removing the cap. After the motor is removed(assuming its an I/O) you may find the transom can be accessed from the inside. You may have to put the new one in 2 pieces or cut back the stringers a bit to fit in the new transom. The stringers may be bad as well so this might not be an issue. If the transom needs to be cut and it comprises of 2 sheets of core (plywood) just do it so the cuts don't meet up. Some might feel removing the cap is a better idea, just my 2 cents......
